Field
The present disclosure relates to ocular filtration devices, systems and methods, and more particularly, to glaucoma treatment devices, systems and methods.
Discussion of the Related Art
Glaucoma is a rapidly growing problem in the industrialized world and presents a leading cause of vision loss and blindness. Currently, glaucoma is the second leading cause of irreversible blindness. Glaucoma prevalence is currently approximately 2.2 million people in the United States and over 60 million worldwide. Despite recent technological and pharmacologic advances in medicine, the number of people losing sight due to glaucoma continues to increase.
In brief, glaucoma is characterized by high intraocular pressures, which over time cause damage to the optic nerve, resulting in loss of peripheral vision in early cases. Later stage disease can lead to loss of central vision and permanent blindness. Treatment is aimed at lowering intraocular pressure.
The current standard of care for treating the blinding complications of glaucoma revolves around topical medications, laser treatments, and surgery for the most advanced cases, all aimed at lowering intraocular pressure. For patients with advanced disease, filtering surgery (e.g., aqueous shunting or trabeculectomy) is often required to prevent vision loss.
With respect to aqueous shunting, implanted glaucoma drainage devices (GDDs) are typically used to create an alternate aqueous pathway from the anterior chamber by shunting aqueous out of the eye through a tube to a subconjunctival bleb or reservoir which is usually connected to a plate under the conjunctiva. A major disadvantage of this surgery is that the aqueous may tend to flow too rapidly out of the tube until a fibrous membrane has encapsulated the reservoir. To this end, medical practitioners may elect to tie off the external portion of the tube or block its lumen with suture or other material, such that once the reservoir has become encapsulated, the suture can be removed. These represent an all-or nothing option with regards to the amount of aqueous flow. Further, some GDDs have a valve which theoretically prevents flow below certain pressures, but cannot be titrated or adjusted by the medical practitioner.
As with conventional GDD implantation, current trabeculectomy surgeries are not titratable by the medical practitioner post-operatively. During surgery, viscoelastic substances may be left in the anterior chamber to slow the rate of aqueous filtration for the first 24-48 hours, or contact lenses placed on the surface of the eye post-operatively to prevent low pressures. Alternatively, the medical practitioner may place sutures over the sclerostomy flap, and can open these with a laser or mechanically. Again, these allow the medical practitioner to either prevent or allow flow, but without precision, often leading to gross under- or over-filtration. This problem contributes to the high rate of surgical failure with these surgeries long-term.
At least in part due to not being titratable, current surgical techniques are plagued by high rates of complications (such as overfiltering and underfiltering, hypotony, choroidal effusions/hemorrhages), with a failure rate of 50% at 5 years. To address this issue, there exist prior art of using biodegradable implants, fibroblast inhibitors, anti-metabolites, and other drugs over the surface of the scleral flap or stainless steel shunts under the scleral flap to encourage continued flow. For example, the Ex-Press Mini Glaucoma Shunt was originally developed by Optonol, Ltd. (Neve Ilan, Israel) for implantation under the conjunctiva for controlling intraocular pressure (IOP). This biocompatible device is almost 3 mm long with an external diameter of approximately 400 microns. It is a non-valved, MRI compatible, stainless steel device with a 50 micron lumen. It has an external disc at one end and a spur-like extension on the other to prevent extrusion.